Visual Studio 2015 is out, and you should of course update as soon as you can. I did, and moved a project under development from VS2013 to VS2015 and started using the new C# 6.0 language features. No issues there. However, when pushing all changes to TeamCity, things broke a bit.

Here are the steps we had to go through to fix it all:

Make sure you have updated to TeamCity version 9 or newer. This adds support for the VS2015 build runner. Before these are added, you'll get syntax problems (example: Invalid token '=' in class, struct, or interface member declaration) and the like, since it doesn't understand C# 6.0. When done, update your build step to use VS 2015.

After this is done, your build agents might tell you about an unmet requirement: MSBuildTools14.0_x86_Path exists. To fix this, install the Microsoft Build Tools 2015 RC (or get the final version when it's out. It doesn't seem to be at the time of writing).

Even after that, I got an error stating error MSB4019: The imported project "C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\WebApplications\ Microsoft.WebApplication.targets" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk.. To fix this, simply copy that folder from your local machine (Where you have installed VS2015, of course) to the server(s) running the TeamCity build agents.